INORGANIC REPLICATION IN ELECTRON MICROSCOPY 



807 



The natural surfaces of sintered thermistor flakes, prepared by heating 

 in air thin (10 ju) sheets of a mixture of NiO and Mn^Os powders, exhibit 

 well defined planes of sizes suitable for electron micrographic study.'^ Flakes 

 sintered briefly at 1175°C were selected as suitable objects for experimental 

 study of replication. They were molded into the surface of Incite blocks at 

 150-160°C and 2500 Ib/in^. They were then dissolved in HC1,§ and replica 



Fig. 6 — A striated region on the surface of a thermistor disk. White line = 0.1 yu. 

 Striations are near the limit of resolution of the silica replica, which is about 400A thick. 



fihns deposited on the plastic molds at pressures not greater than lO""* mm 

 (usually about 2 X 10~^ mm). The replica surface was then scored into 

 small (about 1.5 mm) squares and immersed in ethyl bromide.^f In a few 

 minutes the repHca films drift free and are then ''fished" from the solvent 



19 H. Christensen and C. J. Calbick, Phys.Rev., 74, 1219 (1948). 



§ A one-step process was precluded because some of the replicating materials are soluble 

 in HCl. 



^ Ethyl bromide is not a good solvent for lucite, while chloroform is. Extended tests 

 have produced better results when a poor solvent, which perhaps frees the replica by 

 creeping between it and the plastic mold without appreciable dissolution, is used. 



